The impacts of a Category 4 hurricane (130-156 mph) can include: Catastrophic damage to homes and buildings; mobile homes are destroyed; most large trees are snapped or uprooted; some roads impassable; large areas without power and communication outages.

It's also shaping up as just about a worst-case scenario storm with possible flooding from two different directions.

Harvey is moving slowly and will be stuck over the Texas coast through the middle of next week, which means rainfall measured in feet, not inches.

We're already feeling the effects of Harvey in the Greater Houston Area with a flurry of tornado warnings. There are reports of damage in some areas, including Galveston, the Matagorda County town of Sargent and parts of Fort Bend County. There have been no reports of injuries.

Photos: Tornado touches down in Sargent

A tornado touched down in Sargent, Texas, in Matagorda County on Aug. 25, county officials said.

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A tornado touched down in Sargent, Texas, in Matagorda County on Aug. 25, county officials said.

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In Houston, we could see rainfall of 15 to 20 inches with isolated areas getting up to 30 inches of rainfall by next Wednesday.

"It's possible that some spots could get up to 30 inches of rain -- it won't be everywhere -- but it will be in spots and so those spots that get that much rain, clearly, they will have a very significant flood threat," said KHOU 11 Chief Meteorologist David Paul.

Except for our coastal communities, Harvey's winds and storm surge will not be an issue for Houston. The main concern inland will be rain. Houston is on the "dirty side" of the storm, which means Harvey's outer bands will bring heavy downpours and storms to southeast Texas while Corpus gets hit by the hurricane force winds.

Photos: Texans prepare for Hurricane Harvey

No entry to Matagorda County's Beach Road (FM-2031).

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No entry to Matagorda County's Beach Road (FM-2031).

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There is also concern about the forecast track. Currently Harvey is forecast to slowly make its way north along the Texas coast and arrive in Houston as a tropical storm early next week. This means Houston could get even more heavy rain Tuesday into Wednesday, especially if Harvey continues to move slowly. A Flash Flood Watch is in effect.

As many as 1.25 million Texans could lose power from the storm, according to forecast models at Texas A&M University.

EVACUATIONS

Several counties have already called for mandatory and voluntary evacuations. Locally, Galveston County Judge Mark Henry has issued a voluntary evacuation for residents on Bolivar Peninsula effective Friday, Aug. 25 at 8 a.m. This order includes the unincorporated areas of Port Bolivar, Crystal Beach, High Island and Gilchrist. Residents who rely on medical assistance or those who cannot go without power for an extended period of time are encouraged to leave.

The Brazoria County judge has issued a mandatory evacuation for coastal communities along the Gulf side of the Intracoastal canal. The evacuation is due to an expected 6-10 foot storm surge. There is a voluntary evacuation for low-lying coastal areas inland of the Intracoastal Waterway.